Investigation of ion beam space charge compensation with a 4-grid analyzer

Abstract

Experiments to investigate the space charge compensation of pulsed high-current heavy ion beams are performed at the GSI ion source text benches with a 4-grid analyzer provided by CEA/Saclay. The technical design of the 4-grid analyzer is revised to verify its functionality for measurements at pulsed high-current heavy ion beams. The experimental investigation of space charge compensation processes is needed to increase the performance and quality of current and future accelerator facilities. Measurements are performed directly downstream a triode extraction system mounted to a multi-cusp ion source at a high-current test bench as well as downstream the post-acceleration system of the high-current test injector (HOSTI) with ion energies up to 120 keV/u for helium and argon. At HOSTI, a cold or hot reflex discharge ion source is used to change the conditions for the measurements. The measurements were performed with helium, argon, and xenon and are presented. Results from measurements with single aperture extraction systems are shown.

Study and development of diagnostic systems to characterise the extraction region in SPIDER

“…The main diagnostic present on VICTOR is the RFEA: a sensor able to measure the (positive) ion energy distribution through a set of 4 polarised grids. RFEAs are well known in literature ( [18,19]) and have already been used in other fusion-related experiments (for example in [20,21]). Their working principle is displayed in figure 2: the 4 grids, made of nickel micrometric meshes, act as particle selectors in order to filter them.…”

Neutralisation and transport of negative ion beams: physics and diagnostics

“…Retarding field energy analysers are an indirect non perturbing method, which analyses the particles emitted radially from the beam plasma, and allows to infer the plasma parameters from the energy distribution function of ions and electrons. One of the first examples is described in [155]; the technique is now commonly adopted for measuring the beam compensation degree, often in combination with other techniques [156][157][158]. For instance [159], describes the preparation of the retarding field energy analyser for NIO1; the system was applied to the investigation both of argon ions and electrons in a sputtering magnetron plasma showing the importance of numerical models for the interpretation of experimental results, particularly in collisional regimes, the system will be soon installed in NIO1.…”

Design of an energy analyzer for low energy 1+charged ion beams at RISP Project

“…Some of these analyzers are large in size, must fit into a small beam diagnostic chamber, and are expensive. The most compact device providing high accurate measurement, relatively simple, cost effective and with a high signal-to-noise ratio output is the retarding field energy analyzer (RFEA) [12][13][14], most common for ion beam applications. This kind of analyzer is used to measure the energy distribution of incoming ions with beam energy up to 80 keV [14] by sweeping the voltage on a retarding field grid while measuring the number of ions still penetrating the grid.…”

“…The most compact device providing high accurate measurement, relatively simple, cost effective and with a high signal-to-noise ratio output is the retarding field energy analyzer (RFEA) [12][13][14], most common for ion beam applications. This kind of analyzer is used to measure the energy distribution of incoming ions with beam energy up to 80 keV [14] by sweeping the voltage on a retarding field grid while measuring the number of ions still penetrating the grid. Its resolving power depends on the beam emittance and space charge effects and mainly on its design which undergoes many improvements.…”